How can I model a decorative serving tray?
You can:

Keep only a flat segment, simplify it as much as possible (actually it will depend on if you plan to use a Subdivision Surface modifier at the end) and mirror (enable the Clipping option of the Mirror modifier):



Create an empty a the center of the object, give your object an Array modifier, choose a Count of 8, disable Relative Offset, enbable Object Offset with the empty as Object:



Rotate the empty 45° on the Z axis:



Move the segment so that it doesn't overlap its instances, extrude inwards:



Extrude to give thickness with AltE &gt; Extrude Faces Along Normals:



Make sure you don't create inner faces, if so, delete them:



Add geometry and bvels where needed:



Apply the modifiers, close the center, merge the vertices by distnace, stretch on the X axis: